Researchers from the Washington University School of Medicine in St. Louis have discovered that the Zika virus is able to live on the eyes. The virus' genetic material was also identified in tears.

For a study published in the journal Cell Reports, the researchers used mice models to explain why some infected patients develop eye disease like uveitis, a condition that can lead to a permanent loss in vision. After observing the effects of the Zika virus on the eyes of mouse adults, newborns and fetuses, they want to take the next step in their work with humans.

"We need to consider whether people with Zika have infectious virus in their eyes and how long it actually persists," said Michael S. Diamond, M.D., Ph.D., one of the senior authors for the study.

About a third of babies who acquire the infection in the utero present eye disease in the form of optic nerve inflammation, damage to the retina or blindness. In adults, the virus can lead to conjunctivitis, which is characterized by redness and itchiness, and uveitis in rarer cases.

The researchers were able to show that the Zika virus is alive in mouse eyes after seven days but they were not able to determine how it was able to travel to the eyes.

With eye infection confirmed in the virus, it raises the possibility that Zika could be spread by coming into contact with infected people's tears. While the virus itself was not found in the tears, the researchers did find Zika's genetic material in the sample 28 days after the mice were infected.

According to Jonathan J. Miner, M.D., Ph.D., while the mouse tears did not harbor the live virus, it doesn't mean that it would be the same in humans. He said there might be a certain window when human tears could be highly infectious and those who come into contact with it can facilitate the spread of the virus.

When the researchers move on to human subjects, they want to specifically determine if the live virus can persist in the cornea or other parts of the eye as that can have implications on corneal transplants.

As an immune-privileged site, the eye doesn't get a lot of activity from the immune system to prevent accidental damage to sensitive tissues for vision while fighting off an infection. However, that also means infections can persist in the eyes well after being cleared from the body.

Zika is spreading fast so researchers are on a race to understand all the means of transmission for the virus. Mosquitoes are largely blamed for the spread but Diamond says a number of factors may be at play. And if sexual transmission is not playing a major role, it is possible that some other bodily fluid may be helping the virus' quick spread.

Photo: Walter Wilhelm | Flickr

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